Plant builds bigger shells in acidic water
UC SANTA BARBARA (US) — The future of ocean life for its shelled creatures may not be so bleak, marine scientists say.
As fossil fuel emissions increase, so does the amount of carbon dioxide oceans absorb and dissolve, lowering pH levels.
“As pH declines, there is this concern that marine species that have shells may start dissolving or may have more difficulty making calcium carbonate, the chalky substance that they use to build shells,” says Debora Iglesias-Rodriguez, a professor in the Department of Ecology, Evolution and Marine Biology at the University of California, Santa Barbara.
But researchers discovered that a microscopic shelled plant, Emiliania huxleyi, actually had bigger shells in high carbon dioxide seawater conditions.
“The story years ago was that ocean acidification was going to be bad, really bad for calcifiers,” says Iglesias-Rodriguez.
While the team acknowledges that calcification tends to decline with acidification, “we now know that there are variable responses in sea corals, in sea urchins, in all shelled organisms that we find in the sea.”
These single-celled marine coccolithophore are a large army of ocean-regulating shell producers that create oxygen as they process carbon by photosynthesis and fortify the ocean food chain.
As one of the Earth’s main vaults for environmentally harmful carbon emissions, their survival affects organisms inside and outside the marine system. However, as increasing levels of atmospheric carbon dioxide causes seawater to slide down the pH scale toward acidic levels, this environment could become less hospitable.
Researchers used an approach known as shotgun proteomics to uncover how E. huxleyi’s biochemistry could change in future high carbon dioxide conditions, which were set at four times the current levels for the study. This approach casts a wider investigative net that looks at all changes and influences in the environment as opposed to looking at individual processes like photosynthesis.
Shotgun proteomics examines the type, abundance, and alterations in proteins to understand how a cell’s machinery is conditioned by ocean acidification.
“There is no perfect approach,” said Iglesias-Rodriguez. “They all have their caveats, but we think that this is a way of extracting a lot of information from this system.”
‘Not simply dissolving away’
To mirror natural ocean conditions, the team used over half a ton of seawater to grow the E. huxleyi and bubbled in carbon dioxide to recreate both present day and high future carbon levels. It took more than six months for the team to grow enough plants to accumulate and analyze sufficient proteins.
The team found that E. huxleyi cells exposed to higher carbon dioxide conditions were larger and contained more shell than those grown in current conditions. However, they also found that these larger cells grow slower than those under current carbon dioxide conditions.
Aside from slower growth, the higher carbon dioxide levels did not seem to affect the cells even at the biochemical level, as measured by the shotgun proteomic approach.
“The E. huxleyi increased the amount of calcite they had because they kept calcifying but slowed down division rates,” explains Iglesias-Rodriguez. “You get fewer cells but they look as healthy as those under current ocean conditions, so the shells are not simply dissolving away.”
The team stresses that while representatives of this species seem to have biochemical mechanisms to tolerate even very high levels of carbon dioxide, slower growth could become problematic. If other species grow faster, E. huxleyi could be outnumbered in some areas.
“The cells in this experiment seemed to tolerate future ocean conditions,” says postdoctoral researcher Bethan Jones, who is now at Rutgers University. “However, what will happen to this species in the future is still an open question. Perhaps the grow-slow outcome may end up being their downfall as other species could simply outgrow and replace them.”
The European Project on Ocean Acidification supported the research, which is detailed in a study published in the journal PLOS ONE.
Source: UC Santa Barbara
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